| Silicon carbide porous ceramics are especially promising for aerospace,biomedical and environment with some excellent properties such as high hardness,high strength and excellent thermal stability.Utilize the superior properties of silicon carbide to add the unique structure of biomass carbon in order to prepare new structural and functional integrated materials.In this paper,silicon carbide porous ceramics were prepared through a low temperature catalytic reaction,using biomass carbon?pine wood?as carbon template,and Fe?NO3?3·9H2O,Co?NO3?2·6H2O,Ni?NO3?2·6H2O as catalyst precursor.The effects of the reaction temperature,reaction time,particle size of silica powder,and kinds and contents of catalyst on the phase composition and morphology of the products were investigated.The coupling relationship between the pore structure of product,oxidation resistance and multi-factor preparation was revealed and the reaction mechanism of product was explored.The results indicated that:?1?A layer of SiC whiskers was formed in the surface of the carbon template at1250 ?,using pine wood and silicon powder with different particle sizes as raw materials.The whiskers with SiC/Si O2 shell-core structure and 12 ?m in length were synthesized.Reducing the particle size of silicon powder and increasing the reaction temperature are favorable for the growth of SiC.?2?Compared with the sample without catalyst,the silicon powder could react at a lower temperature in the sample containing a small amount of catalyst.The synthesis temperature can be reduced to 1150 ? with 4 wt% Fe?NO3?3·9H2O under the identical conditions,and the product shows excellent oxidation resistance;The formation of SiC whiskers started with Co?NO3?2·6H2O as catalyst at 1150 ?.At the same time,defects such as stacking faults were found in SiC whiskers in the sample with Co?NO3?2·6H2O.Furthermore,the synthesis temperature of SiC whiskers can be further reduced to 1100 ? in the sample with 5 wt% Ni?NO3?2·6H2O.?3?Low-temperature catalytic preparation of SiC whiskers involves multiple growth mechanisms.With Fe?NO3?3·9H2O as catalyst,the nucleation stage of whiskers is controlled by S-L-S mechanism,and V-L-S mechanism thereafter?growth reaction?.With Co?NO3?2·6H2O as the catalyst,the whisker nucleation stage is controlled by the V-S mechanism and then controlled by the S-L-S mechanism.And the V-S mechanism and the V-L-S mechanism are dominated in growth stage.With Ni?NO3?2·6H2O as catalyst,the nucleation stage of whiskers is dominated by S-L-S mechanism,while the growth of of SiC was mainly established to be gas-gas reaction. |
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